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15 pages, 4255 KiB

Open AccessArticle

Experimental Investigation on the Performance of Historical Squat Masonry Walls Strengthened by UHPC and Reinforced Polymer Mortar Layers

by Bin Peng, Sandong Wei, Libo Long, Qizhen Zheng, Yueqiang Ma and Leiyu Chen

Appl. Sci. 2019, 9(10), 2096; https://doi.org/10.3390/app9102096 - 21 May 2019

Cited by 11 | Viewed by 3385

Abstract

Strengthening historical brick masonry walls is important because these walls are major load-bearing members in many architectural heritages. However, historical brick masonry has low elastic modulus and low strength, historical masonry walls are prone to surface treatment or other structural intervention, and some [...] Read more.

Strengthening historical brick masonry walls is important because these walls are major load-bearing members in many architectural heritages. However, historical brick masonry has low elastic modulus and low strength, historical masonry walls are prone to surface treatment or other structural intervention, and some of the walls lack integrity. These characteristics make effective strengthening of historical masonry walls difficult. To address the issue, strengthening layers made up of ultra-high performance concrete (UHPC) are potentially useful. To investigate the strengthening effect of the UHPC layers, the authors constructed three squat walls using historical bricks and mortar collected from the rehabilitation site of a historical building, and strengthened two of the walls with a UHPC layer and a reinforced polymer mortar layer respectively. The three walls were broken down by horizontal cyclic force along with constant vertical compression, and then the unstrengthened one was strengthened in-situ by a UHPC layer and was tested again. The experimental results indicate that the UHPC layers significantly improved the in-plane shear resistance and cracking load of the squat walls, without decreasing the walls’ ultimate deformation. They effectively strengthened both moderately and severely damaged historical masonry walls, because the UHPC filled the existing damages and improved the integrity of the masonry substrate. In addition, the UHPC layers intervened the historical walls less than the reinforced polymer mortar layer. Therefore, the UHPC layers are efficient in strengthening historical squat masonry walls. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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17 pages, 3882 KiB

Open AccessArticle

Guided Wave-Based Monitoring of Evolution of Fatigue Damage in Glass Fiber/Epoxy Composites

by Gang Yan, Xiang Lu and Jianfei Tang

Appl. Sci. 2019, 9(7), 1394; https://doi.org/10.3390/app9071394 - 3 Apr 2019

Cited by 10 | Viewed by 3200

Abstract

This paper presents an experimental study on detecting and monitoring of evolution of fatigue damage in composites under cyclic loads by using guided waves. Composite specimens fabricated by glass fiber/epoxy laminates and surface mounted with piezoelectric wafers are fatigued under tension–tension loads. A [...] Read more.

This paper presents an experimental study on detecting and monitoring of evolution of fatigue damage in composites under cyclic loads by using guided waves. Composite specimens fabricated by glass fiber/epoxy laminates and surface mounted with piezoelectric wafers are fatigued under tension–tension loads. A laser extensometer is used to obtain the degradation of longitudinal stiffness of the specimens under fatigue states to reflect the accumulation of internal fatigue damage. Meanwhile, at different fatigue cycles, one wafer acts as actuator to excite diagnostic guided waves, and the other acts as sensor to receive corresponding response waves. These guided wave signals are then processed by wavelet packet transform to extract characteristic features of energies in multiple frequency bands. A statistical multivariate outlier analysis is then performed to determine the existence of fatigue damage and to characterize their evolution using Mahalanobis squared distance. Experimental results have demonstrated the potential applicability and effectiveness of guided waves for continuous monitoring of fatigue damage in composite structures. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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12 pages, 3256 KiB

Open AccessArticle

An Omnidirectional Near-Field Comprehensive Damage Detection Method for Composite Structures

by Zhiling Wang, Zhenwei Xiao, Yonglin Li and Yudong Jiang

Appl. Sci. 2019, 9(3), 567; https://doi.org/10.3390/app9030567 - 8 Feb 2019

Cited by 5 | Viewed by 2464

Abstract

As one of the active structural health monitoring methods based on the Lamb wave, the ultrasonic phased-array damage detection method can provide information such as damage location and range more intuitively, which is why this method is a research hotspot in the field [...] Read more.

As one of the active structural health monitoring methods based on the Lamb wave, the ultrasonic phased-array damage detection method can provide information such as damage location and range more intuitively, which is why this method is a research hotspot in the field of Lamb wave-based damage monitoring. However, the ultrasonic phased-array damage detection method intended for the far field is not applicable to near-field damage monitoring. In addition, the traditional one-dimensional piezoelectric phased-array damage imaging method suffers from a blind area in the near field, and the data collection time of its angle scanning is relatively long. In view of these problems, this paper proposes an omnidirectional damage imaging monitoring method, combining the near-field sampling phased-array damage monitoring algorithm and the two-dimensional phased-array. The proposed method is verified by experiments using complex composite materials, and the results obtained show that the proposed omnidirectional near-field sampling phased-array damage imaging method is suitable for real-time damage detection in complex composite materials. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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17 pages, 8371 KiB

Open AccessArticle

Advanced NDT Methods and Data Processing on Industrial CFRP Components

by Vito Dattoma, Francesco Willem Panella, Alessandra Pirinu and Andrea Saponaro

Appl. Sci. 2019, 9(3), 393; https://doi.org/10.3390/app9030393 - 24 Jan 2019

Cited by 21 | Viewed by 4083

Abstract

In this work, enhanced thermal data processing is developed with experimental procedures, improving visualization algorithm for sub-surface defect detection on industrial composites. These materials are prone to successful infrared nondestructive investigation analyses, since defects are easily characterized by temperature response under thermal pulses [...] Read more.

In this work, enhanced thermal data processing is developed with experimental procedures, improving visualization algorithm for sub-surface defect detection on industrial composites. These materials are prone to successful infrared nondestructive investigation analyses, since defects are easily characterized by temperature response under thermal pulses with reliable results. Better defect characterization is achieved analyzing data with refined processing and experimental procedures, providing detailed contrasts maps where defects are better distinguished. Thermal data are analyzed for different CFRP specimens with artificial defects and experimental procedures are verified on real structural aeronautical component with internal anomalies due to impact simulation. A better computation method is found to be useful for simultaneous defect detection by means of automatic mapping of absolute contrast, optimized to identify defect boundaries. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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13 pages, 4503 KiB

Open AccessArticle

Detection and Characterization of Debonding Defects in Aeronautical Honeycomb Sandwich Composites Using Noncontact Air-Coupled Ultrasonic Testing Technique

by Honggang Li and Zhenggan Zhou

Appl. Sci. 2019, 9(2), 283; https://doi.org/10.3390/app9020283 - 15 Jan 2019

Cited by 27 | Viewed by 5401

Abstract

The finite models of honeycomb sandwich composite with intact and embedded debonding defects are constructed. The sound pressure in fluid domain and the stress strain problem in solid domain are related by acoustic-structure coupling method, which visually shows the propagation process and modal [...] Read more.

The finite models of honeycomb sandwich composite with intact and embedded debonding defects are constructed. The sound pressure in fluid domain and the stress strain problem in solid domain are related by acoustic-structure coupling method, which visually shows the propagation process and modal characteristics of the acoustic wave inside the honeycomb sandwich composite. The simulation results show that the transmission longitudinal wave T1 (transmission initial wave) can effectively characterize debonding defects of honeycomb sandwich composite. However, in the actual detection of honeycomb sandwich composite, there are some problems, such as poor Signal-to-noise ratio (SNR) of received signal, incognizable transmission initial wave. In order to solve these problems, this paper proposes to apply polyphase coded pulse compression technique to air-coupled ultrasonic testing system. The actual test results show that the SNR of received signal is effectively improved, the transmission initial wave can be effectively identified, and the compressed signal has a good response to debonding defect. The air-coupled ultrasonic testing C scan result of honeycomb sandwich composite verifies the rationality and correctness of the theoretical simulation and signal processing technique, which promotes industrial application of air-coupled ultrasonic testing technique in the aerospace field. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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16 pages, 6301 KiB

Open AccessArticle

Interface Characterization within a Nuclear Fuel Plate

by James Smith, Clark Scott, Brad Benefiel and Barry Rabin

Appl. Sci. 2019, 9(2), 249; https://doi.org/10.3390/app9020249 - 11 Jan 2019

Cited by 4 | Viewed by 3529

Abstract

To predict the performance of nuclear fuels and materials, irradiated fuel plates must be characterized efficiently and accurately in highly radioactive environments. The characterization must take place remotely and work in settings largely inhospitable to modern digital instrumentation. Characterization techniques based on non-contacting [...] Read more.

To predict the performance of nuclear fuels and materials, irradiated fuel plates must be characterized efficiently and accurately in highly radioactive environments. The characterization must take place remotely and work in settings largely inhospitable to modern digital instrumentation. Characterization techniques based on non-contacting laser sensing methods enable remote operation in a robust manner within a hot-cell environment. Laser characterization instrumentation can offer high spatial resolution and remain effective for scanning large areas. A laser shock (LS) system is currently being developed as a post-irradiation examination (PIE) technique in the hot fuel examination facility (HFEF) at the Idaho National Laboratory (INL). The laser shock technique will characterize material properties and failure loads/mechanisms in various composite components and materials such as plate fuel and next-generation fuel forms in high radiation areas. The laser shock-technique induces large amplitude shock waves to mechanically characterize interfaces such as the fuel–clad bond. As part of the laser shock system, a laser-based ultrasonic C-scan system will be used to detect and characterize debonding caused by the application of the laser shock. The laser shock system has been used to characterize the resulting bond strength within plate fuels which have been fabricated using different fabrication processes. The results of this study will be to select the fabrication process that provides the strongest interface. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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15 pages, 4180 KiB

Open AccessArticle

An Efficient Time Reversal Method for Lamb Wave-Based Baseline-Free Damage Detection in Composite Laminates

by Liping Huang, Junmin Du, Feiyu Chen and Liang Zeng

Appl. Sci. 2019, 9(1), 11; https://doi.org/10.3390/app9010011 - 20 Dec 2018

Cited by 12 | Viewed by 3457

Abstract

Time reversal (TR) concept is widely used for Lamb wave-based damage detection. However, the time reversal process (TRP) faces the challenge that it requires two actuating-sensing steps and requires the extraction of re-emitted and reconstructed waveforms. In this study, the effects of the [...] Read more.

Time reversal (TR) concept is widely used for Lamb wave-based damage detection. However, the time reversal process (TRP) faces the challenge that it requires two actuating-sensing steps and requires the extraction of re-emitted and reconstructed waveforms. In this study, the effects of the two extracted components on the performance of TRP are studied experimentally. The results show that the two time intervals, in which the waveforms are extracted, have great influence on the accuracy of damage detection of the time reversal method (TRM). What is more, it requires a large number of experiments to determine these two time intervals. Therefore, this paper proposed an efficient time reversal method (ETRM). Firstly, a broadband excitation is applied to obtain response at a wide range of frequencies, and ridge reconstruction based on inverse short-time Fourier transform is applied to extract desired mode components from the broadband response. Subsequently, deconvolution is used to extract narrow-band reconstructed signal. In this method, the reconstructed signal can be easily obtained without determining the two time intervals. Besides, the reconstructed signals related to a series of different excitations could be obtained through only one actuating-sensing step. Finally, the effectiveness of the ETRM for damage detection in composite laminates is verified through experiments. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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19 pages, 9360 KiB

Open AccessArticle

A Full-Process Numerical Analyzing Method of Low-Velocity Impact Damage and Residual Strength for Stitched Composites

by Hongjian Zhang, Mingming Wang, Weidong Wen, Ying Xu, Haitao Cui and Jinbo Chen

Appl. Sci. 2018, 8(12), 2698; https://doi.org/10.3390/app8122698 - 19 Dec 2018

Cited by 1 | Viewed by 3482

Abstract

The failure and residual strength after low-velocity impact of stitched composites are very important in their service and maintenance phases. In order to capture the failure and residual strength more accurately, a full-process numerical analyzing method was developed in this paper. The full-process [...] Read more.

The failure and residual strength after low-velocity impact of stitched composites are very important in their service and maintenance phases. In order to capture the failure and residual strength more accurately, a full-process numerical analyzing method was developed in this paper. The full-process numerical analyzing method includes two parts: (1) Part 1 is the progressive low-velocity impact damage prediction method for stitched composites; (2) Part 2 is the progressive residual strength prediction method by introducing all types of damage that are caused by the low-velocity impact as the analysis presuppositions. Subsequently, the failure and residual strength of G0827/QY9512 stitched composites were simulated by the full-process numerical analyzing method. When compared with experiments, it is found that: (1) the maximum error of low-velocity impact damage areas was 17.8%, and their damage modes were similar; (2) the maximum error of residual strength was 8.9%. At last, the influence rules of stitched density and stitching thread thickness were analyzed. The simulation results showed that, if there is no suture breakage failure, stitched density affects the mechanical properties of the stitched composites, while stitching thread thickness has little effect on it; otherwise, both factors have a significant effect on the mechanical properties. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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14 pages, 5248 KiB

Open AccessArticle

Acoustic Emission Based on Cluster and Sentry Function to Monitor Tensile Progressive Damage of Carbon Fiber Woven Composites

by Wei Zhou, Peng-fei Zhang and Yan-nan Zhang

Appl. Sci. 2018, 8(11), 2265; https://doi.org/10.3390/app8112265 - 16 Nov 2018

Cited by 31 | Viewed by 4279

Abstract

Understanding the tensile failure mechanisms in carbon fiber woven composites based on the acoustic emission (AE) technique is a challenging task. In this study, the mechanical behaviors of composites were studied under uniaxial tensile loading. Meanwhile, the internal damage evolution process in composites [...] Read more.

Understanding the tensile failure mechanisms in carbon fiber woven composites based on the acoustic emission (AE) technique is a challenging task. In this study, the mechanical behaviors of composites were studied under uniaxial tensile loading. Meanwhile, the internal damage evolution process in composites was monitored by AE and the recorded AE signals were analyzed. To achieve the dominant damage mechanisms in composites, five AE parameters such as rise time, duration, energy, peak amplitude, and frequency were selected for cluster analysis by a k-means algorithm. The results show that AE signals can be divided into three clusters based on microscopic observations and frequency range. The three clusters correspond to three kinds of damage modes such as matrix cracking, fiber/matrix debonding, and fiber breakage. In addition, the sentry function (SF) was adopted to investigate AE signals originated from the internal damage evolution in composites. It was found that the drop in the SF curve corresponds to the serious damage of the composites. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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20 pages, 4348 KiB

Open AccessArticle

Multiaxial Damage Characterization of Carbon/Epoxy Angle-Ply Laminates under Static Tension by Combining In Situ Microscopy with Acoustic Emission

by Kalliopi-Artemi Kalteremidou, Brendan R. Murray, Eleni Tsangouri, Dimitrios G. Aggelis, Danny Van Hemelrijck and Lincy Pyl

Appl. Sci. 2018, 8(11), 2021; https://doi.org/10.3390/app8112021 - 23 Oct 2018

Cited by 17 | Viewed by 2957

Abstract

Investigating the damage progression in carbon/epoxy composites is still a challenging task, even after years of analysis and study. Especially when multiaxial stress states occur, the development of damage is a stochastic phenomenon. In the current work, a combined nondestructive methodology is proposed [...] Read more.

Investigating the damage progression in carbon/epoxy composites is still a challenging task, even after years of analysis and study. Especially when multiaxial stress states occur, the development of damage is a stochastic phenomenon. In the current work, a combined nondestructive methodology is proposed in order to investigate the damage from the static tensile loading of carbon fiber reinforced epoxy composites. Flat angle-ply laminates are used to examine the influence of multiaxial stress states on the mechanical performance. In situ microscopy is combined with acoustic emission in order to qualitatively and quantitatively estimate the damage sequence in the laminates. At the same time, digital image correlation is used as a supporting tool for strain measurements and damage indications. Significant conclusions are drawn, highlighting the dominant influence of shear loading, leading to the deduction that the development of accurate damage criteria is of paramount importance. The data presented in the current manuscript is used during ongoing research as input for the damage characterization of the same material under fatigue loads. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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17 pages, 5089 KiB

Open AccessArticle

Challenges and Limitations in the Identification of Acoustic Emission Signature of Damage Mechanisms in Composites Materials

by Nathalie Godin, Pascal Reynaud and Gilbert Fantozzi

Appl. Sci. 2018, 8(8), 1267; https://doi.org/10.3390/app8081267 - 31 Jul 2018

Cited by 52 | Viewed by 5149

Abstract

Acoustic emission is a part of structural health monitoring (SHM) and prognostic health management (PHM). This approach is mainly based on the activity rate and acoustic emission (AE) features, which are sensitive to the severity of the damage mechanism. A major issue in [...] Read more.

Acoustic emission is a part of structural health monitoring (SHM) and prognostic health management (PHM). This approach is mainly based on the activity rate and acoustic emission (AE) features, which are sensitive to the severity of the damage mechanism. A major issue in the use of AE technique is to associate each AE signal with a specific damage mechanism. This approach often uses classification algorithms to gather signals into classes as a function of parameters values measured on the signals. Each class is then linked to a specific damage mechanism. Nevertheless, each recorded signal depends on the source mechanism features but the stress waves resulting from the microstructural changes depend on the propagation and acquisition (attenuation, damping, surface interactions, sensor characteristics and coupling). There is no universal classification between several damage mechanisms. The aim of this study is the assessment of the influence of the type of sensors and of the propagation distance on the waveforms parameters and on signals clustering. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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16 pages, 5017 KiB

Open AccessArticle

The Influence of Sensor Size on Acoustic Emission Waveforms—A Numerical Study

by Eleni Tsangouri and Dimitrios G. Aggelis

Appl. Sci. 2018, 8(2), 168; https://doi.org/10.3390/app8020168 - 25 Jan 2018

Cited by 14 | Viewed by 4504

Abstract

The performance of Acoustic Emission technique is governed by the measuring efficiency of the piezoelectric sensors usually mounted on the structure surface. In the case of damage of bulk materials or plates, the sensors receive the acoustic waveforms of which the frequency and [...] Read more.

The performance of Acoustic Emission technique is governed by the measuring efficiency of the piezoelectric sensors usually mounted on the structure surface. In the case of damage of bulk materials or plates, the sensors receive the acoustic waveforms of which the frequency and shape are correlated to the damage mode. This numerical study measures the waveforms received by point, medium and large size sensors and evaluates the effect of sensor size on the acoustic emission signals. Simulations are the only way to quantify the effect of sensor size ensuring that the frequency response of the different sensors is uniform. The cases of horizontal (on the same surface), vertical and diagonal excitation are numerically simulated, and the corresponding elastic wave displacement is measured for different sizes of sensors. It is shown that large size sensors significantly affect the wave magnitude and content in both time and frequency domains and especially in the case of surface wave excitation. The coherence between the original and received waveform is quantified and the numerical findings are experimentally supported. It is concluded that sensors with a size larger than half the size of the excitation wavelength start to seriously influence the accuracy of the AE waveform. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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Review

Jump to: Research

21 pages, 5243 KiB

Open AccessReview

Digital Shearography for NDT: Phase Measurement Technique and Recent Developments

by Qihan Zhao, Xizuo Dan, Fangyuan Sun, Yonghong Wang, Sijin Wu and Lianxiang Yang

Appl. Sci. 2018, 8(12), 2662; https://doi.org/10.3390/app8122662 - 18 Dec 2018

Cited by 72 | Viewed by 11006

Abstract

Composite materials have seen widespread use in the aerospace industry and are becoming increasingly popular in the automotive industry due to their high strength and low weight characteristics. The increasing usage of composite materials has resulted in the need for more effective techniques [...] Read more.

Composite materials have seen widespread use in the aerospace industry and are becoming increasingly popular in the automotive industry due to their high strength and low weight characteristics. The increasing usage of composite materials has resulted in the need for more effective techniques for nondestructive testing (NDT) of composite structures. Of these techniques, digital shearography is one the most sensitive and accurate methods for NDT. Digital shearography can directly measure strain with high sensitivity when combined with different optical setups, phase-shift techniques, and algorithms. Its simple setup and less sensitivity to environmental disturbances make it particularly well suited for practical NDT applications. This paper provides a review of the phase measurement technique and recent developments in digital shearographic NDT. The introduction of new techniques has expanded the range of digital shearography applications and made it possible to measure larger fields and detect more directional or deeper defects. At the same time, shearography for different materials is also under research, including specular surface materials, metallic materials, etc. Through the discussion of recent developments, the future development trend of digital shearography is analyzed, and the potentials and limitations are demonstrated. Full article

(This article belongs to the Special Issue Damage Inspection of Composite Structures)

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